World Health Organisation chief Margaret Chan on Friday accused "ruthless, devious" tobacco companies of bullying as she battled attempts to stimulate smoking in poor nations.
In a speech marking the fifth anniversary of an international convention on tobacco control, Chan said she would not allow the tobacco industry to take part in talks on expanding the world's first public health treaty.
"Like my predecessors, I am not on speaking terms with the tobacco industry, but I will say this: we've come a long way, bullies," she said at WHO headquarters in Geneva.
The 2005 convention bans advertising and sponsorship, advocates tobacco taxes, legislation to make public places smoke-free and other restrictions to stifle a growth in smoking which is blamed for increasing heart disease, strokes and cancers.
"The battle against opposition continues, especially in developing countries," the UN health chief said.
"It is estimated that tobacco use kills more than five million people per year -- an average of one person every six seconds -- and accounts for one in 10 adult deaths worldwide," she added.
Chan said the treaty backed by 168 countries had allowed the agency and public health authorities to stand up against the "ruthless, devious, rich and powerful" tobacco industry.
While tobacco use in many affluent countries had dropped significantly, others have been slow to implement tobacco restrictions, according to the WHO.
"Most alarming of all, tobacco use is actually increasing in many developing countries. If Big Tobacco is in retreat in some parts of the world, it is on the march in others," Chan said.
Developing countries were the "new frontier" for tobacco marketing, but were also the most vulnerable to its ill-effects and chronic disease due to the shortage of health care and poverty, she added.
"In these countries as elsewhere, girls and women are a market with attractive and lucrative growth potential, and they are likewise being targeted," said Chan.
Some 5.4 percent of the world's population can benefit from laws against smoking in public places, according to the WHO.
Such bans were enforced in 17 countries, with Colombia, Djibouti, Guatemala, Mauritius, Panama, Turkey, and Zambia joining the list in 2008, the WHO said in December.
Twenty-one countries have high taxes -- above 75 percent -- on tobacco products.
The agency said Friday that more than 90 countries have prohibited the sale of cigarettes and tobacco products to minors, while at least 80 have introduced "large, clear and visible" health warnings on packages.
The global death toll attributed to tobacco could rise to eight million by 2030 at the current rate.